1. Field of the Invention
This invention pertains generally to systems and methods for generating images of three dimensional objects for navigation purposes, and more particularly to systems and methods for generating such images in medical and surgical applications.
2. Description of the Background Art
Precise imaging of portions of the anatomy is an increasingly important technique in the medical and surgical fields. In order to lessen the trauma to a patient caused by invasive surgery, techniques have been developed for performing surgical procedures within the body through small incisions with minimal invasion. These procedures generally require the surgeon to operate on portions of the anatomy that are not directly visible, or can be seen only with difficulty. Furthermore, some parts of the body contain extremely complex or small structures and it is necessary to enhance the visibility of these structures to enable the surgeon to perform more delicate procedures. In addition, planning such procedures requires the evaluation of the location and orientation of these structures within the body in order to determine the optimal surgical trajectory.
New diagnostic techniques have been developed in recent years to obtain images of internal anatomical structures. These techniques offer great advantages in comparison with the traditional X-ray methods. Newer techniques include microimpulse radar (MIR), computer tomography (CT) scans, magnetic resonance imaging (MRI), positron emission tomography (PET), ultrasound (US) scans, and a variety of other techniques. Each of these methods has advantages and drawbacks in comparison with other techniques. For example, the MRI technique is useful for generating three-dimensional images, but it is only practical for certain types of tissue, while CT scans are useful for generating images of other anatomical structures. Ultrasound scanning, in contrast, is a relatively rapid procedure; however it is limited in its accuracy and signal-to-noise ratio.
The imaging problem is especially acute in the field of neurosurgery, which involves performing delicate surgical procedures inside the skull of the patient. The above techniques have improved the surgeon""s ability to locate precisely various anatomical features from images of structures within the skull. However this has only limited usefulness in the operating room setting, since it is necessary to match what the surgeon sees on the 2D image with the actual 3D patient on the operating table. The neurosurgeon is still compelled to rely to a considerable extent on his or her knowledge of human anatomy.
The stereotactic technique was developed many years ago to address this problem. In stereotactic surgery, a frame of reference is attached to the patient""s head which provides reference points for the diagnostic images. The device further includes guides for channeling the surgical tool along a desired trajectory to the target lesion within the brain. This method is cumbersome and has the drawback that the surgeon cannot actually see the structures through which the trajectory is passing. There is always the risk of damage to obstacles in the path of the incision, such as portions of the vascular or ventricular system. In essence, with previous neurosurgical techniques the surgeon is in the position much like that of a captain piloting a vessel traveling in heavy fog through waters that have many hazards, such as shoals, reefs, outcroppings of rocks, icebergs, etc. Even though the captain may have a very good map of these hazards, nevertheless there is the constant problem of keeping track of the precise location of the vessel on the map. In the same way, the neurosurgeon having an accurate image scan showing the structures within the brain must still be able to precisely locate where the actual surgical trajectory lies on the image in order to navigate successfully to the target location. In the operating room setting, it is further necessary that this correlation can be carried out without interfering with the numerous other activities that must be performed by the surgeon.
The navigation problem has been addressed in U.S. Pat. No. 5,383,454, issued Jan. 24, 1995 (Bucholz). This patent describes a system for indicating the position of a surgical probe within a head on an image of the head. The system utilizes a stereotactic frame to provide reference points, and to provide means for measuring the position of the probe tip relative to these reference points. This information is converted into an image by means of a computer.
U.S. Pat. No. 5,230,623, issued Jul. 27, 1993 (Guthrie), discloses an operating pointer whose position can be detected and read out on a computer and associated graphics display. The pointer can also be used as a xe2x80x9c3D mousexe2x80x9d to enable the surgeon to control the operation of the computer without releasing the pointer.
U.S. Pat. No. 5,617,857, issued Apr. 8, 1997 (Chader et al.) sets forth an imaging system and method for interactively tracking the position of a medical instrument by means of a position-detecting system. The pointer includes small light-emitting diodes (LED), and a stationary array of radiation sensors is provided for detecting pulses emitted by these LED""s and utilizing this information to ascertain dynamically the position of the pointer. Reference is made also to U.S. Pat. No. 5,622,170, issued Apr. 22, 1997 (Schulz), which describes a similar system connected to a computer display for displaying the position of an invasive surgical probe relative to a model image of the object being probed (such as a brain).
U.S. Pat. No. 5,531,227, issued Jul. 2, 1996 (Schneider) explicitly addresses the problem recognized in many other references that it is desirable to provide a real time display of a surgical probe as it navigates through the brain. This patent describes a system for providing images along the line of sight of the surgeon in a dynamic real-time fashion. In this system the images that are displayed are resliced images from a three-dimensional data reconstruction which are sections or slices orthogonal to the line of sight, taken at various positions along this line specified by the user. Thus, while the viewpoint for the line of sight is always external to the body, the sectional planes that are used to define the virtual images may constitute various slices through the body chosen by the surgeon. These images may be superimposed on actual images obtained by an image recording device directed along the line of sight such as a video camera attached to the surgeon""s head, and the composite images may be displayed.
The systems described above attempt to address the navigation problem in various ways, and they all have the common drawback of requiring a certain level of abstract visualization by the surgeon during an operating room procedure. When the surgeon is proceeding through the brain toward a target tumor or lesion, it is desirable to be fully aware of all of the structures around the surgical trajectory. With previous systems the displays that are presented do not provide all of this is information in a single convenient real-time display, and they require the viewer to piece together and re-orient the displayed information to obtain a mental picture of the surrounding structures. These are serious practical disadvantages in an operating room setting. What is absent from previous systems is a 3D display that shows, in a real-time view, the various structures looking ahead from the surgical probe along a line of sight into the brain in three and two dimensions, including structures hidden by other features.
The present invention provides an improved system and method for displaying 3D images of anatomical structures in real time during surgery to enable the surgeon to navigate.through these structures during the performance of surgical procedures. This system is also useful in planning of surgical procedures. The system includes a computer with a display and input devices such as a keyboard and mouse. The system also includes a position tracking system that is connected both to the computer and also to the surgical probes or other instruments that are used by the surgeon. The position tracking system provides continual real time data to the computer indicating the location and orientation of the surgical instrument in use. The computer further includes a memory containing patient data produced by imaging scans, such as CT or MRI scans, from which 2-dimensional and 3-dimensional images of the anatomical structure may be generated. Means are provided for registration of these images with respect to the patient.
The computer memory is further provided with programs that control the generation of these anatomical images. These programs include software for segmentation of the scan images to identify various types of structures and tissues, as well as the reconstruction of 2D and 3D images from the scan data. This software allows these images to be displayed with various magnifications and orientations, and with various sectional views produced by slice planes in various locations and orientations, all controlled by the surgeon.
This image-generating software has the important feature that it produces 3D images that are perspective views of the anatomical structures, with user-controlled means for varying the viewing orientation and location, and also varying the displayed transparency or opacity of various types of tissues, structures, and surfaces in the viewed region of interest. This enables the user to effectively xe2x80x9csee throughxe2x80x9d surfaces and structures in the line of sight of the image to reveal other structures that would otherwise be hidden in that particular view.
Further, the images are generated from the viewpoint of the surgical probe or instrument that is in use, looking from the tip of the instrument along its longitudinal axis. Thus, when an invasive surgical instrument such as a scalpel or forceps is inserted into an incision in the body, the display provides a three dimensional perspective view of anatomical structures from a viewpoint inside the body. These images are all generated in real time xe2x80x9con the flyxe2x80x9d. Thus, as the instrument is moved or rotated, the position tracking system continually provides data to the computer indicating the location and orientation of the instrument, and the displayed image is continually updated to show the structures toward which the instrument is pointing.
In addition, for probes or instruments being used that are capable themselves of generating images, such as ultrasound probes, endoscopes, or surgical.microscopes, the system provides means for integrating these images with those generated from the scan data. The software enables the user to overlay the xe2x80x9cactual imagesxe2x80x9d generated by these instruments with the xe2x80x9cvirtual imagesxe2x80x9d generated from the scan data.
It is an object of this invention to provide a system and method for generating an image in three dimensional perspective of anatomical structures encountered by a surgeon during the performance of surgical procedures.
A second object of this invention is to provide a system and method for generating such an image with user-controlled means for varying the location and orientation of the viewpoint corresponding to the image.
Another object of this invention is to provide a system and method for generating such an image with user-controlled means for varying the opacity of structures and surfaces in the viewed region of interest, so that the displayed image shows structures and features that would be otherwise hidden in a normal view.
Yet another object of this invention is to provide a system and method for generating such an image with a viewpoint located at the tip of the instrument being used by the surgeon in the direction along the longitudinal axis of the instrument.
Still another object of this invention is to provide a system and method for generating such an image in real time, such that the displayed image continually corresponds to the position of the instrument being used by the surgeon.
Yet a further object of this invention is to provide a system and method for comparing and combining such an image with the image produced by an image-generating instrument being used by the surgeon.